The PSTN/ISDN Switch Off

What do I need to know?


Publish Date:

7 June 2024

BT’s 2027 switch-off of PSTN and ISDN services marks a crucial shift in telecommunications. As part of BT’s digital voice changeover plan requires all to have an internet connection. Trustack is here to guide you through this transition with urgency and clarity.


BT’s original projected switch-off date (2025) has been extended, with the aim to complete the move by the end of January 2027. The extension is no reason to delay as migrating from analogue to digital as quickly and effectively as possible is important


In 2027 BT is switching off their Public Switched Telephone Network (PSTN) and Integrated Services Digital Network(ISDN) services. This change will affect all residential and business customers and aligns with the Government’s promise to see 15 million premises connected to fibre by 2027. 


For businesses, it will not only mean that your phone services are affected but also services that run on your phone lines using the PSTN network. This will include services such as EPOS machines, alarm monitoring services, fire monitoring services, and lift emergency phones.

Close-up image of several data cables or fibers with illuminated binary code patterns (ones and zeroes) on them, resembling an ISDN network. The background is a soft blue gradient, giving the image a high-tech and futuristic feel.

Why is it happening?

It is not only in the UK that the migration to digital is taking place. As technology evolves, phone companies around the world are adapting. The switch-off is already underway in countries like Germany, Japan, and Sweden, with Estonia and the Netherlands already having completely switched off their networks.


Technology has evolved significantly and quite simply the PSTN network has become outdated and costly to maintain.

What are the alternatives?

Of course, the retiring of the telephone network as we know it would not be happening if there was no new technology to replace it. Over the last several years, telephone systems have been developed to use IP. This allows telephone systems to use standard Internet connections. Along with this new technology are many new terms and technologies including:


  • VoIP: stands for Voice over Internet Protocol and allows you to make and receive phone calls over the Internet.
  • SIP: stands for Session Initiation Protocol and rather than just sending voice data like the VoIP phone system, SIP will send and receive any multimedia data such as video calls.
  • 4G &5G: With the development of 4G and 5G networks across the UK, another alternative is to use your mobile phone as your main point of contact rather than having a traditional landline.

What are the benefits?

Moving to this newer technology offers the same benefits as we see now and some new ones. 

A digital illustration depicting a PSTN concept. Various devices, including a tablet, smartphone, computer, and security camera, are connected to a central PSTN label, representing an intricate network communication system. The design subtly hints at the transition from ISDN to modern networking technologies.


Reduced costs

Call statistics


Greater choice of telephone hardware. You can continue to use a telephone handset as well as mobile phones, tablets, laptops, PCs and Macs.


Telephone systems can easily scale along with your requirements. Whether it is simply an additional user, or a brand-new office location. At its simplest form, you simply require Internet connectivity.

Quick changes

Changes can be implemented quicker e.g. call routing and diverts.

When do I need to act and how do I prepare for the switch off?

Many businesses have already adopted a digital model, moving their communications to the cloud, making calls over the internet and embracing video conferencing. If you have the supporting infrastructure, then there is no reason why an educated and planned migration to digital lines cannot be considered now.

Preparing your business for the upcoming PSTN switch off in 2027 is essential to ensure a smooth transition.

Here are some steps you can take to prepare:

  • Assess your current communication infrastructure: Identify all the equipment and systems that rely on the PSTN or ISDN. This includes phones, fax machines, alarms, EPOS machines, door entry systems, and CCTV. Make a comprehensive list of these devices.
  • Research alternative communication solutions: Explore alternative options that will replace the PSTN and ISDN. Look for digital solutions such as Voice over IP (VoIP) or Session Initiation Protocol (SIP) that can provide voice and data services over the internet. Consider consulting with a telecommunications provider to understand the available options.
  • Evaluate your broadband capabilities: Since the switch to a digital network may require an upgrade in broadband services, assess your current internet connection. Determine if it can handle the increased data traffic and bandwidth requirements of the new system. If necessary, contact your internet service provider to discuss possible upgrades.
  • Plan for equipment replacement: Once you have identified the equipment that will become obsolete, create a plan for replacing or upgrading it. Contact the manufacturers or suppliers of these devices to understand their compatibility with digital networks and explore potential replacements.
  • Consider security implications: As you transition to a digital network, consider the security implications of the new communication systems. Ensure that your new infrastructure has appropriate security measures in place to protect your data and communication channels.
  • Develop a migration timeline: Create a detailed timeline for migrating your communication systems to the new digital network. Consider any potential disruptions or downtime during the transition and plan accordingly to minimize any negative impact on your business operations.
  • Train your staff: Provide training and support to your employees to familiarise them with the new communication systems. Ensure they understand the changes, know how to operate the new equipment, and are aware of any new features or capabilities.
  • Test and monitor the new system: Before the switch off date, conduct thorough testing of the new communication infrastructure to identify and resolve any issues or compatibility problems. Monitor the performance of the new system to ensure it meets your business requirements.

Trustack's recommendations

“The 2025 PSTN Switch Off represents the biggest shake up of modern-day Telecommunications that will affect Business and Domestic Users alike.


My recommendation would be to have your PSTN/ISDN to SIP migration done and dusted well before the deadline date, not only to beat the inevitable rush nearer to the Switch Off, but also to take advantage of the cost savings with SIP and advancement of features and facilities with modern Hosted UC systems.”


‍- Tom Hassan, Unified Communications and Telephony Consultant

Frequently Asked Questions Around the PSTN/ISDN Switch Off

How can I be prepared for the 2027 PSTN Switch Off?

Ensuring that your current telephony system can support SIP Trunking or opt for a Hosted Telephony Service.

Will I be able to have a fast broadband connection at home?

Yes, however, you will have to upgrade to either FTTP (Fibre to the Premises) or to SoGEA (Single order Generic Ethernet Access). With SoGEA you only get a broadband data service and no telephone line. Therefore, for telephone service, you will have to have a connection to a hosted phone system, or an IP based phone system.

What is the benefit of SoGEA?

Depending on location, SoGEA can provide downloads of up to 80Mbs using the current FTTC technology.

After the 2027 PSTN Switch off can I still use my existing telephony equipment such as fax, DECT phone etc at home?

Yes, with a hosted phone system and ATAadapter. Connecting these traditional analogue devices to a SIP to Analogue convertor (ATA), will enable them to register on the hosted phone system.

What happens if I haven’t migrated to SIP in December 2027?

Any business or consumer who hasn’t migrated to an alternative telephony service will be left without service.

What happened in 2023?

In September 2023 Openreach will no longer supply single PSTN lines, ISDN2, ISDN30 or add additional channels to existing services. For more information on the switch-off contact us

It is important to start to think about your move sooner rather than later

There could be a lot to plan for and resources to do this will become limited nearer the deadline date.

Get your business on the front foot

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About the Authors
Emma Phillips

Marketing Executive